Reception in FM

When I switched to FM reception mode, I recognized the background noise creating the lines as coming from my computer monitor. Turning it off cleared up most all of the lines you see in the other posts, but it's hard to run my tests in the dark...

Reception in LSB

Reception in USB

As received in CW mode

TX and RX combo baseline

Noise in the TX and RX as seen on DigiPan. No audio, wavering on lower frequency traces from noise in the TX power supply.

Equiment Used

To generate audio tones, I used DigiPan v1.6d on a laptop computer. The audio transformer on the QRP transformer is plugged into the amplifier speaker output on the front. I copied a short bit of text from the DidiPan help file and placed it in the transmit window to be sent. I use a Kenwood TS-570D to receive, the antenna is a short piece of wire from a Heathkit 2m field strength meter. The antenna being amongst electronic devices also adds noise to the system. The transmitter operates into a 50 Ohm load.

Quick Initial Test

My first test. The buffer in the TX was getting hot so I limited my test to a few seconds. I have since added heatsinks which allows me several minutes of TX time. The extra lines are AC noise in the transmitter circuit from the latop and poorly filter power supply. This is a quick test to see if it can be done, no shielding, no filters.

DigiPan Baseline

I have a problem with a ground loop creating noise in the soundcard with this set-up, so I took a baseline reading of what to expect to see on DigiPan before I start.

Audio transformer varactor modification.

Here is the transformer and the cut trace of the varactor circuit. 0 - 14 VDC still passes through the transformer to control the transmitter frequency. The transformer adds about 100 Ohms to the circuit.

Initial Design Idea.

Within fifteen minutes I had dug up two generic QRP kits and a 2400 Bd ISA modem with a nice 1:1 audio transformer. One kit didn't work. I didn't want to waste time trouble-shooting it, so I tried the second one, a 20m TX. 20m rig works fine, varactor circuit works fine, now for a quick modification. A copy of the schematic for the 80m rig that didn't work is above. Aside from component values, design of the 20m rig is the same. It would appear that the easiest way to modulate this CW TX would be to alter the voltage and frequency between the wiper of R1 and where it connects with R2 and C1.

Initial Request

Hank Greeb asks a question:

Sent: Thursday, December 27, 2007 15:18
Subject: FSK-31 vs PSK-31

"If I key a crystal oscillator with pure FSK at the same rate and similar frequency change as is produced when the phase is changed with PSK-31, will it produce a waveform which can be decoded by a PSK-31 receiver? I say this because, if this were the case, it would appear that one could generate PSK-31 with almost any CW rig with a varactor across the oscillator circuit. 72/73 de n8xx Hg p.s. Happy Gnu Yaer 2 all"

He had asked a couple of years earlier. I don't recall if he got flack for the idea or if there was no interest. I had though about doing the same and commented on it at the time, but never got around to trying it. Time to see what happens.